Pickup electrode with rigid electrolyte cup

ABSTRACT

An electrode for attachment to the skin is made from an adhesively coated, elastic sheet sandwiched between a nonconducting, low profile cup member and a clamp plate fixed in assembled relation by a conductive snap fastener member extending therethrough. Both the cup member and the clamp plate are in the form of cavity washers, the confronting margins of which squeeze the sheet. In use, the cup member cooperates with the skin to form an enclosed cavity for an electrolyte. When pressed against the skin, the elastic sheet resiliently urges the cup member against the skin.

O r United States Patent 1 [111 3,713,435 Szpur [451 Jan. 30, 1973 s41PICKUP ELECTRODE WITH RIGID 3,340,868 9/1967 Darling ..l28/2.06 E

ELECTROLYTE CUP 3,505,993 4/1970 Lewes et al. ..l28/2.06 E

[75] Inventor: Roman Szpur, Dayton, Ohio Primary Examiner wmiam E- Kamm[73] Assignee: NDM Corporation, Dayton, Ohio Att0rneyH. Talman Dybvig[22] Filed: June 5, 1972 ABSTRACT [2H Appl' 259563 An electrode forattachment to the skin is made from Related US, Ap licati D t anadhesively coated, elastic sheet sandwiched 63 between a nomconducting,low profile cup member 1 com'nuauonofser'No' and a clamp plate fixed inassembled relation by a conductive snap fastener member extending [21:]..128/2.06l;1{6l12b8/54l)Z therethmugh Both the cup member and the clamph d R 2 plate are in the form of cavity washers, the confrontgg g Z 6ing margins of which squeeze the sheet. in use, the

cup member cooperates with the skin to form an enclosed cavity for anelectrolyte. When pressed against [56] References cued the skin, theelastic sheet resiliently urges the cup NI STATES PATENTS member againstthe skin.

1,583,087 5/1926 Morse ..l28/4l7 5 Claims, 4 Drawing Figures PICKUPELECTRODE WITH RIGID ELECTROLYTE CUP This is a continuation ofapplication Ser. No. 1 1,208 filed Feb. 13, 1970.

BACKGROUND OF THE INVENTION This invention relates to medical electrodesof the type used to detect electrical signals from the skin of a livingsubject and more particularly to the type of such electrode which isdesigned for use over several days without interferring with thesubjects normal activities.

The electrode of this invention is designed for use with commerciallyavailable electrolytes in the form of electrode pastes or gels. It isknown that the conductor portions of such electrodes should be spacedfrom the skin of the subject by the electrolyte to obtain the leastresistance and to minimize motion artifacts or noise. Optimum resultsare obtained when the volume of electrolyte and its areas of contactover the skin and the conductor portion of the electrode remainconstant.

Electrodes have been made with barriers to prevent contact between theskin and their conductor portions. The barriers are provided with smallapertures to be filled with an electrolyte. Although such devices mayminimize artifacts, they are difficult and thus costly to construct, andthe imposition of the apertured barrier undesirably reduces conductionbetween the skin and the conductor portion of the electrode.

Other electrodes have been made without any barrier between the skin andthe electrode conductor. For the most part these have been designed toprovide electrical contact with only a very small skin area. One type ofelectrode provides for contact over a relatively large skin area. Toobtain the necessary isolation between the metal conductor and the skin,these electrodes have a relatively high profile, that is, a large heightto diameter ratio. However, low profile electrodes are preferred tominimize the possibility of movement of the electrolyte, which may causespurious signals, and to minimize the inconvenience experienced by thesubjects wearing the electrodes.

SUMMARY OF THE INVENTION The electrode of this invention is providedwith a relatively rigid, non-conductive, low profile cup member having aconvexly curved rim and placed in an inverted position on the skin ofthe subject. The cup member is effectively clamped to the skin by anoverlying elastic sheet having a pressure sensitive adhesive surroundingthe cup member. When attached to the skin, the elastic sheet resilientlypresses the cup member against the skin to firmly hold the cup member ina fixed position. Separation of the elastic sheet from the cup member isprevented by a clamp plate positioned on top of the sheet. The conductorportion of the electrode includes a thin conductive plate located in thecavity between the cup member and the skin, the conductive plateabutting the base of the cup member. The entire cup member can be filledwith an electrolyte to provide a broad area of contact over the skin.

For simplicity of construction, the conductor comprises a snap fastenermember projecting through the cup member, the carrier sheet and theclamp plate to hold these parts in assembled relation. Also, the clampplate is preferably constructed identically to the cup member, bothbeing similar to cavity washers. The confronting margins of the cupmember and the clamp plate squeeze and annular portion of the elasticsheet thereby to assist in holding the center portion of the elasticsheet under tension when the lower surface of the elastic sheet isadhered to the skin.

The elastic sheet is desirably a sponge like material,

preferably open cell polyvinylchloride, because such material may bestretched in all directions and has an elastic character. When usingopen cell polyvinylchloride sheet or the like it is desired that boththe upper and lower surfaces have a relatively closed cell construction.A partially closed cell construction is desired on the lower surface tobetter form a barrier layer for receiving a pressure sensitive adhesive.The top surface is preferably closed cell because closed cell surfacesdo not retain dirt as readily as open cell material. The relativelyclosed cell surfaces also contribute to the elasticity of the sheetwhich is necessary to maintain the cup member pressed against the skin.A sheet made from open cell polyvinylchloride with partially closed cellupper and lower surfaces also has the advantages of being inexpensive,soft to the touch and pleasing in appearance. Air readily passes throughsuch material to ventilate the skin. When an electrode in accordancewith this invention is adhered to the skin, even for extended periods ofuse, substantially the only sensation experienced by the subject is thetackiness of the adhesive.

Generally stated, it is an object of this invention to provide animproved, low-profile, inexpensive medical electrode and especially onefor use over extended periods of time. Other objects and advantages willbecome apparent from the drawing and the following description.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of anelectrode made in accordance with this invention shown applied to thehand of a subject;

FIG. 2 is a cross sectional view of the electrode, taken along line 2-2of FIG. I, applied to the skin;

FIG. 3 is an exploded perspective view of an electrode in accordancewith this invention and a protective sheet for the adhesive prior toassembly of these parts; and

FIG. 4 is a cross sectional view of an electrode made in accordance withthis invention with a different type of protective member.

DESCRIPTION OF THE PREFERRED EMBODIMENT An electrode generallydesignated 10 made in accordance with this invention is shown secured tothe hand H of a subject in FIGS. 1 and 2. The electrode 10 consists of acircular, elastic pad or sheet 12 overlying a centrally located,inverted cup member 14, a clamp plate 16 located on top of the sheet 12in alignment with the inverted cup member 14, and a metallic conductorformed from a male snap fastener member, generally designated 18. Theannular area of the lower surface of the sheet 12 in surroundingrelation to the cup member 14 is provided with a pressure sensitiveadhesive layer 20 for attachment of the electrode 10 to the skin. Inuse, electrical signals from the skin are amplified and sensed byapparatus (not shown) connected to the snap fastener member 18 by aconductive lead and cooperating snap fastener member, shown by phantomlines 18a. The electrical path is from the skin through an electrolyteconfined in a chamber or cavity 42 enclosed by the cup member 14 and theskin, and thence through the snap fastener member 18.

With reference to FIGS. 2 and 3, the cup member 14 is in the form of acavity washer and has a circular flat base 22 surrounded by an annularflange 24 which is semicircular or U-shaped in cross section. The centerof the cup base 22 is apertured as indicated at 26. The cup member 14 iselectrically non-conductive and can be vacuum formed from a relativelythin sheet of a suitable thermoplastic such as vinyl, linearpolyethylene, cellulose acetate butyrate, or the like.

The clamp plate 16 is also non-conductive and is preferably identicallyconstructed to the cup member 14 and accordingly includes a circularflat base 28 with a U-shaped rim or flange 30 and has a central aperture32. As will become apparent, the shape of the clamp plate 16 is notcritical but the shape illustrated is preferred because of the savingsin manufacturing costs resulting from use of the same parts for both thecup member 14 and the clamp plate 16.

The male snap fastener member 18 comprises a lower circular plateportion 34 from the center of which a hollow, open ended stud 36 isformed upwardly, and an upper plate portion 38 having an upwardlyprotruding, hollow socket 40. To assemble the parts forming theelectrode 10, the cup member 14 and the clamp plate 16 are firstcentrally located and aligned on opposite sides of the sheet 12. Thestud 36 is then inserted through the aperture 26, pierced through thecenter of the sheet 12 and then through the aperture 32 into the socket40. The parts of the snap fastener member 18 are then pressed togetherwhereupon the upper end of the stud 36 folds inwardly and its side wallscollapse outwardly, causing the fastener member parts to be tightlywedged together. The snap fastener 18 is metal and, as well known tothose skilled in the art, preferably has a coating or plating of silveror the like composition to provide a satisfactory electrical interfacewith the electrolyte confined in the cavity or chamber 42.

The adhesive layer may be applied to the lower surface of the sheet 12either before or after assembly. After the parts are assembled and theadhesive layer 20 applied, a protective waxed paper sheet 44 having acentral cutout 46 for the cup member 14 is applied to the bottom of thesheet 12. The electrode 10 with the protective sheet 44 may then bestored until ready for use. An alternative arrangement is shown in FIG.4 wherein the cup member 14 is loaded with the electrolyte at the timeof assembly and a suitably formed plastic or paper protective sheet 48is applied in covering relation to both the lower surface of the sheet12 and the cup member 14 to retain the electrolyte therein. Of course,the protective sheet 44 or the protective sheet 48 are easily removableat the time the electrode 10 is to be used.

As noted above, the metallic snap fastener 18, which is the onlyconductor portion of the electrode 10, should be supported away fromcontact with the skin. The area between the snap fastener 18 and theskin should be completely filled with the electrolyte.

Further, the movement of the electrode relative to the skin and theelectrolyte should be positively restricted. In addition to satisfyingthese requirements, the electrode 10 of this invention has an unusuallylow profile. These characteristics result primarily from the use of theelastic sheet 12 and the design of the cup member As apparent from aninspection of FIG. 2, the semicircular or U-shaped flange 24 forms aconvexly curved rim defining the mouth of the cup member 14 and an outerwall, designated 50, diverging outwardly from the rim. The upper marginof the outer wall 50 is substantially coplanar with the upper surface ofthe base 26. The central portion of the elastic sheet is tightlycompressed between the confronting base surfaces of the cup member 14and the clamp plate 16. Accordingly, prior to attachment of theelectrode 10 to the skin, the sheet 12 and its adhesive layer 20 areaxially spaced above the rim of the cup member 14. In order to attachthe electrode 10 to the skin, the sheet 12 must be flexed downwardly,whereupon the annular portion of the sheet 12 immediately surroundingthe outer wall 50 is stretched to span the area between the upper,marginal edge of the diverging outer wall 50 and the portion of the skinto which the adhesive layer 20 is secured. Because of its elasticnature, the stretched portion of the sheet 12 resiliently presses theconvexly curved rim formed by the flange 24 into the skin, creating aslight depression therein. As a result, the cup member 14 is firmlyretained in sealing relation to the skin, thereby positively confiningthe electrolyte within the cavity or chamber 42. Also, movement of thecup member 14 and the electrolyte relative to the skin is avoided. TheU-shaped flange has a sufficient depth to create a minimal, but adequatespacing between the skin and the conductive lower plate 34 of the snapfastener member 18 within the cavity 42. Because movements of the cupmember 14 are restricted, the spacing between the plate portion 34 andthe skin is maintainedover long periods of use.

For reasons already mentioned, the elastic sheet 12 is preferably formedfrom a foamed or open cell polyvinylchloride having relatively closedcell upper and lower surfaces. This type of material can be obtained ata low cost, is sufficiently flexible to conform to the skin, and hassufficient elasticity to press the cup member 14 against the skinwithout tearing or pulling away from the skin. As those familiar withsuch material are aware, the two surfaces of foamed polyvinylchloridesheets are typically of a slightly different nature, one having a moreclosed cell construction than the other. Although these surfaces areinterchangeable in the manufacture of the electrode 10, it is presentlypreferred that the more open cell surface be lowermost. The more opencell surface is sufficiently porous to provide for adequate aeration orventilation of the skin it covers, which is especially important for useover extended periods of time. Also, the more closed cell surface ispreferably uppermost because this type of surface is resistant tosoiling.

The various thermoplastic materials mentioned above for use in formingthe cup member 14 and the clamp plate 16 are ideal for this purposebecause they are inexpensive, non-conductive, and can easily be vacuumformed to the desired shape. Although of a flexible nature, athermoplastic sheet is adequately rigid when formed to the illustratedcup shape to prevent collapse of the outer wall 50 under the force ofthe stretched sheet 12. The axial spacing of the rim and the uppermargin of the cup member 14 are thus maintained. A thermoplastic sheetalso has a resiliency which assists in forming a good seal with theparts of the snap fastener member 18. Accordingly, the electrolyte isretained entirely within the chamber 42 and the hollow center of thesnap fastener member 18. Since both the cup member 14 and the clampplate 16 are identically constructed of sheet material, the confrontingmargins of their outer walls compress the elastic sheet 12 therebetween,as indicated at 52. Therefore, substantially the only portion of thesheet 12 which is stretched when applied to the skin is that portionbetween the outer wall 50 and the skin.

An electrode in accordance with this invention has been made andsuccessfully tested. The electrode had an overall height on the order ofonly 0.3 inch with the depth of the cup member 14 on the order of 0.094inch and the elastic sheet 12 having a thickness of 0.125 inch. Thediameter of the elastic sheet 12 was 2% inch. The cup member 14, andaccordingly the clamp member 16, had an overall diameter of 0.875 inchwith the diameter of the base 22 being one-half inch. The lower snapfastener plate 34 had a diameter of 0.406 inch. These dimensions are notcritical. For example, the overall diameter of the cup member could bebetween approximately one-half inch and 1 inch with correspondingvariations in the diameter of the cup base 22 and the snap fastenerplate 34. Unless the cup member 14 is made deeper, approximately 1 inchis deemed to be the maximum acceptable cup diameter because the skinbounded by the rim of a larger diameter cup member would likely engagethe conductive plate portion 34.

Commercially available medical grade acrylic pressure sensitive adhesivewas applied to the lower surface of the elastic sheet 12 to form theadhesive layer 20. Because the lower surface of the elastic sheet 12 isnot completely impervious, some of the adhesive may have migratedharmlessly beyond the partially closed cell surface. A sufficientlysmall quantity of the adhesive was applied to avoid closing the lowersurface to the passage of air. Of course, the adhesive layer could beobtained in other ways. However, the adhesive layer should be pressuresensitive so that the elastic sheet 12 is stretched as a natural resultof the pressing of the sheet 12 onto the skin. Also, the adhesive layershould not be of such a nature that it adversely affects theskinconforming flexibility of the elastic sheet or that it closes thepores of the lower surface of the elastic sheet l2.

The diameter of the illustrated elastic sheet 12 is approximately twoand one-half times the diameter of the cup member 14. It is preferredthat the diameter of the carrier sheet 12 be on the order of two tothree times the diameter of the cup member 14 to provide a broad skincontact area for the pressure sensitive adhesive layer 20. Because thecarrier sheet 12 is flexible it readily conforms to movements of theskin. Although the cup member 14 is relatively inflexible, it issufficiently firmly held against the skin by the tension in thestretched portion of the carrier sheet 12 that the electrode of thisinvention can be used on sub ects engaged in strenuous exercise.

Although a preferred embodiment of this invention has been described, itwill be understood that various changes may be made within the scope ofthe appended claims.

Having thus described my invention, I claim:

1. In a medical electrode, a low profile non-conducting, relativelyrigid, collapse resistant cup member having a base and a rim, aperturedelastic sheet means connected to said cup member and overlying said rim,adhesive on the lower surface of said sheet means adjacent and insurrounding relation to said rim, a snap fastener projecting throughsaid base and supported by said base remote from said rim, said snapfastener projecting through an aperture in said sheet means, electrolytemeans contacting said snap fastener and substantially filling said cupmember, and a removable protective cover for said adhesive.

2. In a medical electrode, a low profile non-conducting, relativelyrigid, collapse resistant cup member having a base and a rim, sheetmeans connected to said cup member and surrounding said rim, adhesive onthe lower surface of said sheet means adjacent said rim, a snap fastenerprojecting through said base and supported by said base remote from saidrim, said snap fastener projecting through an aperture in said sheetmeans, and removable protective cover for said adhesive.

3. The medical electrode of claim 2 including electrolyte meanscontacting said snap fastener and substantially filling the interior ofsaid cup member.

4. In a medical electrode, a low profile non-conducting, relativelyrigid, collapse resistant cup member having a base and a rim, sheetmeans connected to said cup member and surrounding said rim, an adhesiveon the lower surface of said sheet means adjacent to said rim, a snapfastener projecting through said base and supported by said base remotefrom said rim, and a removable protective cover for said adhesive.

5. The medical electrode of claim 4 including electrolyte meanscontacting said snap fastener and substantially filling the interior ofsaid cup member.

Disclaimer 3,7l3,435.-R0man Szpur, Dayton, Ohio. PICKUP ELECTRODE WITHRIG- ID ELECTROLYTE CUP. Patent dated Jan. 30, 1973. Disclaimer filedAug. 25, 1983, by the assignee, NDM Corp. Hereby enters this disclaimerto all claims of said patent.

[Official Gazette October 25, 1983.]

1. In a medical electrode, a low profile non-conducting, relatively rigid, collapse resistant cup member having a base and a rim, apertured elastic sheet means connected to said cup member and overlying said rim, adhesive on the lower surface of said sheet means adjacent and in surrounding relation to said rim, a snap fastener projecting through said base and supported by said base remote from said rim, said snap fastener projecting through an aperture in said sheet means, electrolyte means contacting said snap fastener and substantially filling said cup member, and a removable protective cover for said adhesive.
 2. In a medical electrode, a low profile non-conducting, relatively rigid, collapse resistant cup member having a base and a rim, sheet means connected to said cup member and surrounding said rim, adhesive on the lower surface of said sheet means adjacent said rim, a snap fastener projecting through said base and supported by said base remote from said rim, said snap fastener projecting through an aperture in said sheet means, and removable protective cover for said adhesive.
 3. The medical electrode of claim 2 including electrolyte means contacting said snap fastener and substantially filling the interior of said cup member.
 4. In a medical electrode, a low profile non-conducting, relatively rigid, collapse resistant cup member having a base and a rim, sheet means connected to said cup member and surrounding said rim, an adhesive on the lower surface of said sheet means adjacent to said rim, a snap fastener projecting through said base and supported by said base remote from said rim, and a removable protective cover for said adhesive. 